Conventionally, there are devices each being installed to a bicycle and calculating and displaying information relating to the traveling of the bicycle, information relating to the exercise of a driver, and the like. A device of such a type receives data from a sensor installed to the bicycle and calculates and displays predetermined information. As examples of the information that is displayed, there are a force (torque or the like) that is applied by the driver to a pedal and the like. As a method of measuring a force of such a type, for example, in Patent Literature 1, a technology for detecting torque applied to a crank by measuring a strain of a crankshaft has been disclosed.
In addition, in Patent Literature 2, a technology for embedding a piezoelectric sensor inside a crank and measuring torque based on a voltage generated according to a strain of the crank has been disclosed.
Furthermore, Patent Literature 1 describes that the technology is also applicable to a stationary bicycle-type health machine (also referred to as a bicycle ergometer or an exercise bike).
As above, in a manpower machine including a crank, it is known to calculate momentum and the like by measuring torque by detecting a strain applied to the crank.